Lawn Herbicide Exposure to Dogs

Considerable interest has been generated by a recently published study by PCOP scientists and key collaborators at Purdue University and the University of North Carolina. The purpose of the study was to determine the extent to which lawn chemicals are taken into the body of dogs and eliminated in the urine. This study was in followup to an earlier study that showed a significant association between lawn chemical exposure and increased bladder cancer risk in dogs with a strong genetic risk for the cancer, i.e. Scottish terriers. Briefly, in the new study 3 different herbicides (2,4-D, MCPP, dithiopyr) were measured in the urine of dogs of any breed that did not have cancer and on the surface of the grass in 25 households who had already planned to apply lawn chemicals and in 8 households who were not going to apply lawn chemicals. The 3 chemicals were selected because they are commonly used in lawn chemical mixtures, not because of specific known carcinogenic effects of those chemicals. The goal was to assess how readily lawn chemicals are taken up by dogs, as well as to assess factors that could result in prolonged presence of the chemicals on the grass.

Some of the important findings and conclusions are summarized below:

Lawn chemical exposure was widespread in dogs. At least 1 of the 3 chemicals measured in the study was present in the urine of dogs in the majority of the 25 households after lawn chemicals were applied to the grass.

“Untreated” grass also contained lawn chemicals, presumably from drift from nearby treated areas. At least 1 of the 3 chemicals was detected on the grass in 7 of 8 control households, as well as in many of the “treated” households BEFORE the chemicals were applied.

Half of the dogs living in “untreated” control households had lawn chemicals in their urine.

The condition of the grass affected how long the chemicals persisted on the surface of the grass where they would be taken up by dogs. Chemicals persist longer on dry brown grass. Chemicals were detected on the grass at 48 hours after treatment in the household study.

The levels of chemicals in the urine were lower than those that would cause acute toxicity. The effects of chronic long term exposure to these levels of chemicals have not yet been determined.

The bottom line is dogs can internalize lawn chemicals from exposure to their treated lawn, exposure to their untreated but contaminated lawn, and from other treated areas such as parks. Further studies are indicated to determine the exposure levels in humans, especially for people involved in yard work, gardening, and sports.

What can pet owners do to reduce exposure to their dogs? Limit lawn chemical use to areas necessary. Consider treating the lawn in sections: the front yard one week, the back yard another week so there is an area for the dog that has not recently been treated. Follow manufacturer or applicator instructions, and do not apply excessive amounts of chemicals. Keep the dog off treated areas for at least as long as the manufacturer recommends, and recognize that longer is usually better. Dogs in our study picked up chemicals from lawns even when the chemicals had dried. Some dedicated dog owners even wash their dogs feet each time they come in the house from the lawn.